net: xilinx: axienet: Support adjusting coalesce settings while running

net: xilinx: axienet: Support adjusting coalesce settings while running

In preparation for adaptive IRQ coalescing, we first need to support
adjusting the settings at runtime. The existing code doesn't require any
locking because

- dma_start is the only function that modifies rx/tx_dma_cr. It is
  always called with IRQs and NAPI disabled, so nothing else is touching
  the hardware.
- The IRQs don't race with poll, since the latter is a softirq.
- The IRQs don't race with dma_stop since they both just clear the
  control registers.
- dma_stop doesn't race with poll since the former is called with NAPI
  disabled.

However, once we introduce another function that modifies rx/tx_dma_cr,
we need to have some locking to prevent races. Introduce two locks to
protect these variables and their registers.

The control register values are now generated where the coalescing
settings are set. Converting coalescing settings to control register
values may require sleeping because of clk_get_rate. However, the
read/modify/write of the control registers themselves can't sleep
because it needs to happen in IRQ context. By pre-calculating the
control register values, we avoid introducing an additional mutex.

Since axienet_dma_start writes the control settings when it runs, we
don't bother updating the CR registers when rx/tx_dma_started is false.
This prevents any issues from writing to the control registers in the
middle of a reset sequence.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Link: https://patch.msgid.link/20250206201036.1516800-3-sean.anderson@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>